The present invention relates to a method and system that is useful to authenticate security paper. Specifically, the present invention relates to a method and system that allows security paper to be authenticated more than once without destroying the authentication mechanism.
Certain types of documents are potentially liable to attempts at counterfeiting. Such documents include checks, travelers"" checks, money orders, bankers drafts, bearer bonds, share certificates, stamps, postal orders, and lottery tickets. Many methods exist that allow verification of the authenticity of these types of documents by the person to whom the document might be presented, in order to make the documents secure. For example, one method involves printing an image such as a multiplicity of dots on paper using a starch containing solution and developing the image with an iodine solution. Such a method is disclosed in U.S. Pat. No. 6,214,766 to Kurrle. The starch solution is colorless until exposed to the iodine. However, once the iodine solution has been applied, the printed image is irreversibly revealed.
Another method for authenticating documents involves printing the document with ink that responds to a change in temperature or pressure. U.S. Pat. No. 5,636,874 to Singer teaches once such method. In Singer, the document is printed with thermochromic ink that responds to a change in temperature over an image of a similar color. The thermochromic ink is activated by heat, such as by rubbing, and the ink changes from colored to colorless revealing the printed image underneath. Once the heat is removed, the ink will regain its color. However, the ink can prematurely change color when exposed to a heat source such as being left in a car or being copied on a photo copier. Additionally, the ink can degrade over time, and the degradation can render the security feature useless.
Systems that utilize ultraviolet light also appear in the prior art. One such system is taught by U.S. Pat. No. 5,421,869 to Gundijian et al. The Gundijian system utilizes a substrate that has a first marking fluid applied to it that is invisible to the human eye under both visible and ultraviolet light. A second marking fluid is then applied that causes a reaction with the first marking fluid. The reaction produces fluorescence that is only visible under ultraviolet light. A drawback to this system is the requirement of an ultraviolet light source for verification of authenticity.
Thus, there is a need for a method and system of making a document secure wherein the authentication procedure does not mar the document, the procedure is repeatable, and the procedure does not require costly equipment, and for a document for use in such a method and system in which the document is durable and unchanged by authentication.
This need is met by the present invention wherein a method and system for authenticating a document is disclosed. The method and system allow the authentication process to be performed numerous times without degradation. The authentication method does not stain or mar the paper.
In accordance with one embodiment of the present invention, a method for authenticating security paper is provided. The method comprises placing an authenticating solution comprising an acid-base indicator in non-ionic form on at least one surface of the security paper and applying an activating solution to the surface containing the authenticating solution. The authenticating solution has an original pH. The activating solution comprises an acid or base that is selected to produce a characteristic color change of the acid-base indicator. The color change only lasts until the activating solution dries. Once this drying occurs, the color change is no longer visible. Typically, the acid-base indicator is selected to be colorless at the original pH of the authenticating solution.
The acid-base indicator may be selected from phenolphthalein, thymolphthalein, fluorescein, xcex1-naptholphthalein and o-cresophthalein and combinations thereof. The concentration of the acid-base indicator is generally less than about 15 percent by weight, and more typically is less than about 5 percent by weight. If one of these indicators is selected, the activating solution may further comprise water as a carrier and a base to cause the desired pH change. The base may be selected from isopropylamine, ethylaamine, diethylamine, butylamine, 3-methoxy propylamine and ammonia and combinations thereof. The concentration of the base selected from this group will generally be in the range of 0.5 to 5 percent by weight. The base may also be selected from sodium hydroxide, potassium hydroxide and ammonia or combinations thereof. The concentration of sodium hydroxide or potassium hydroxide is less than about 0.5 percent by weight, and the concentration of ammonia is less than about 5 percent 5 by weight.
The authenticating solution may be placed on the security paper by printing. The authenticating solution may be printed on the security paper in such a way as to form an invisible image that becomes visible only when the activating solution is applied. Alternatively, the authenticating solution may be printed on the security paper to form a spot coating or a full document flood coating. The printing may comprise flexographic printing. The authenticating solution may further comprise a toner receptive component. The toner receptive component may comprise a toner receptive polymer, and the toner receptive polymer may be selected from styrene-acrylic polymers, acrylic polymers, styrene-butadiene polymers, polyurethane polymers, starch grafted polymers and combinations thereof. The toner receptive polymer may be selected from a styrene-acrylic with a Tg of about 15xc2x0 C. to about 50xc2x0 C. and an acid number of about 25 to about 75, and the authenticating solution may be placed on the security paper by flexographic printing. The toner receptive component may be a resin, and the resin may comprise a maleated phenolic modified resin. The authenticating solution may further comprise an oil when the toner receptive component is a resin and may be printed on the security paper by letterpress printing. The activating solution may be contained in a pen and applied to the security paper by marking with the pen to cause the color change of the authenticating solution.
In accordance with another embodiment of the present invention, a security paper authenticating system is provided. The system comprises a security paper having an authenticating solution on at least one surface of the security paper and an activating solution. The authenticating solution comprises an acid-base indicator in non-ionic form and has an original pH. The activating solution comprises as acid or base, and, on applying the activating solution to the security paper, a color change occurs that reverses when the activating solution dries. The acid or base of the activating solution is selected to produce the characteristic color change of the acid-base indicator in the authenticating solution.
Generally, the acid-base indicator is colorless at the original pH of the authenticating solution, The acid-base indicator may be selected from phenolphthalein, thymolphthalein, fluorescein, xcex1-naptholphthalein and o-cresophthalein and combinations thereof. The concentration of the acid-base indicator may be less than about 15 percent by weight and is more typically less than about 5 percent by weight. When the acid-base indicator is selected from such a group, the activating solution may further comprise water as a carrier and a base. The base may be selected from isopropylamine, ethylamine, diethylamine, butylamine, 3-methoxy propylamine and ammonia, and the base will generally have a concentration in the range of 0.5 to 5 percent by weight. Alternatively the base may be selected from sodium hydroxide, potassium hydroxide and ammonia and combinations thereof The concentration of sodium hydroxide or potassium hydroxide may be less than about 0.5 percent by weight and the concentration of ammonia may be less than about 5 percent by weight.
The authenticating solution may be placed on the security paper by printing. The printing may comprise flexographic printing. The authenticating solution may form an invisible image on the surface of the security paper. Alternatively, the authenticating solution may form a spot coating or fill document flood coating on the surface of the security paper. The authenticating solution may further comprise a toner receptive component. The toner receptive component may comprise a toner receptive polymer, and the toner receptive polymer may be selected from styrene-acrylic polymers, acrylic polymers, styrene-butadiene polymers, polyurethane polymers, starch grafted polymers and combinations thereof. The toner receptive polymer may be selected from a styrene-acrylic with a Tg of about 15xc2x0 C. to about 50xc2x0 C. and an acid number of about 25 to about 75. The authenticating solution with a toner receptive polymer may be placed on the security paper by flexographic printing. The toner receptive component may be a resin, and the resin may comprise a maleated phenolic modified resin. The authenticating solution may further comprise an oil when the toner receptive component is a resin and the authenticating solution may be printed on the security paper by letterpress printing. The activating solution may be contained in a pen and may be applied to the security paper by marking with the pen.
Accordingly, it is an object of the present invention to provide a method and system of authenticating a document that is reversible and reusable. A further object of the present invention is to provide a system and method of authenticating a document that does not leave a mark on the document. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.